1. Field of the Invention
The present invention relates to a fuel cut-off valve that is attached to an upper portion of a fuel tank and connects and disconnects inside with and from outside of the fuel tank according to the fuel level in the fuel tank.
2. Description of the Related Art
Fuel cut-off valves are generally structured to open and close the conduit for leading the fuel vapor to a canister and exert various functions in the open state and the closed state of the conduit. Known fuel cut-off valves have a backflow prevention function to close the conduit at a fuel level close to the full level of a fuel tank and thereby control any further fuel supply with a pressure sensing-type refueling gun and a leakage protection function to prevent the liquid fuel from flowing into the conduit (see, for example, Patent Documents 1 and 2).
Patent Document 1: Japanese Patent No. 3201253
Patent Document 2: Japanese Patent Laid-Open Gazette No. 2002-4966
The fuel cut-off valve disclosed in Patent Document 1 has two valve plugs in separate valve chests. One valve plug opens and closes a vent conduit 22a, whereas the other valve plug opens and closes an orifice conduit 26 connecting with the vent conduit 22a. The fuel cut-off valve disclosed in Patent Document 2 has two valve plugs in separate valve chests. One valve plug opens and closes a valve port 66 according to the fuel level in a fuel tank, whereas the other valve plug placed outside the fuel tank opens and closes an opening 70 between the valve port 66 and a vent conduit 67. These proposed fuel cut-off valves attain both the backflow prevention function and the leakage protection function by closing of the flow path with the two valve plugs.
In the fuel cut-off valve of Patent Document 1, the orifice conduit 26 is linked to the vent conduit 22a in the upstream of the open and close position of the vent conduit 22a with the corresponding valve plug. A vehicle may abruptly turns or rolls on the rough road surface. Such an abrupt turn or roll may adversely affect the closing property of the valve plug and may cause imperfect closing of the flow path with the valve plug. The layout of the flow path in this prior art structure may cause the liquid fuel from directly entering the vent conduit 22a or entering the vent conduit 22a via the orifice conduit 26. This prior art structure accordingly has the low reliability of the leakage protection function. The high production accuracy of the respective elements of the valve plug closing mechanism and the high assembly accuracy are required to ensure the sufficient leakage protection function.
In the fuel cut-off valve of Patent Document 2, the closed state of the valve port 66 located in the fuel tank almost perfectly blocks the ventilation from the tank to the canister. This causes an abrupt increase in inner pressure of the fuel tank. An abrupt expansion of the compressed fuel vapor may lead to the backflow of the fuel or may delay the stop timing of the fuel supply with a refueling gun and cause the liquid fuel from flowing over a fill port. This prior art fuel cut-off valve thus additionally requires a separate backflow prevention mechanism.